<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        button {
          width: 60px;
          height: 30px;
          outline: none;
        }
      </style>
</head>
<body>
    <button id="changeColor">change</button>
    <script src="popup.js"></script>

</body>
</html>